This invention relates to door latches and more particularly, to a door latch mechanism for emergency exit doors.
Applicant is aware of the following U.S. patents, the disclosures of which are incorporated by reference herein.
U.S. Pat. No. 1,203,116 PA1 U.S. Pat. No. 1,430,905 PA1 U.S. Pat. No. 1,706,486 PA1 U.S. Pat. No. 3,325,203 PA1 U.S. Pat. No. 3,189,142 PA1 U.S. Pat. No. 3,705,379 PA1 U.S. Pat. No. 3,819,213 PA1 U.S. Pat. No. 3,869,159 PA1 U.S. Pat. No. 4,007,954 PA1 U.S. Pat. No. 4,015,869 PA1 U.S. Pat. No. 4,083,590 PA1 U.S. Pat. No. 4,311,329 PA1 U.S. Pat. No. 1,253,545 PA1 U.S. Pat. No. 1,612,480 PA1 U.S. Pat. No. 2,824,440 PA1 U.S. Pat. No. 3,335,509 PA1 U.S. Pat. No. 3,477,260 PA1 U.S. Pat. No. 3,811,717 PA1 U.S. Pat. No. 3,854,763 PA1 U.S. Pat. No. 3,877,262 PA1 U.S. Pat. No. 4,012,066 PA1 U.S. Pat. No. 4,074,548 PA1 U.S. Pat. No. 4,183,565 PA1 U.S. Pat. No. 4,384,738
Emergency exit doors, as typically known in the art, serve the function of providing access from a building or area only under certain extraordinary situations. Most of the time these doors remain closed and it is a particular requirement of such doors that they be tamperproof, i.e. not openable by unauthorized persons using a credit card, pry bar or other tool. While the need for their tamperproof feature or "dead lock" is apparent, at the same time, this feature should not unduly complicate the latching and unlatching mechanism or else the possibility of this mechanism jamming or becoming otherwise inoperative increases. And, despite the importance of foregoing, it is also important to avoid impractical and costly alternatives such as having the the deadlock mechanism separate from the latching mechanism.
Certain doors, such as those in schools and other public buildings, must remain locked during a fire in order to prevent its spread. This means the latching mechanism must include a fire or heat responsive element, a fusible material, which renders the latching mechanism inoperative in the presence of a fire or intense heat. The material, or a portion of the mechanism using it, must be easily activated in the event of a fire to make the door unoperable while, under more usual circumstances, not interferring with normal functioning of the latch mechanism.
Finally, the latching mechanism itself should be simple so the deadlock and fusible element integrate easily with it. The mechanism should be readily installed on a door, and once installed, should require little or no maintenance for proper operation.
The present invention is advantageous in that it provides a latching mechanism for emergency exit doors that is readily installed on the door. The mechanism incorporates a latch bolt that moves along a line of action to engage or disengage a door strike, then allowing the door to be closed and opened. The mechanism also incorporates a dead lock feature that blocks movement of the latch bolt along its line of action to provide a relatively simple, yet effective, dead lock that prevents tampering. The latch also includes a release mechanism which disengages the dead lock so the door can be opened at the necessary or proper times. This release mechanism also restores the dead lock when it is intended for the door not to be operable.
In addition to the above, the latch has a fusible lock feature that operates in the presence of fire or intense heat to make the release mechanism inoperable. Consequently the door cannot be opened in these situations. At all other times, however, the fusible lock does not interfere with operation of the release and opening or closing of the door.
The latch preferably has an upper and a lower latch bolt which engage respective upper and lower door strikes. Each latch bolt has an associated dead lock and the release mechanism is designed to operate both dead locks simultaneously to enable the door to be opened and to restore them simultaneously when it is intended that the door not be opened.